This invention relates generally to nuclear reactors, and, more particularly, to a retaining tool for a reactor refueling mast.
A boiling water reactor (BWR) includes a reactor core submerged in water in a closed reactor pressure vessel (RPV). The RPV is disposed in a containment vessel above which is disposed a refueling pool of water. During a refueling cycle, the upper head of the pressure vessel is removed along with internal components of the RPV to provide access to the reactor core. Water completely fills the open vessel up to the level of the pool disposed above, and a conventional mobile refueling gantry or platform is movable above the pool for carrying replacement fuel bundles to the reactor core and removing fuel bundles from the reactor core. The platform typically travels longitudinally on rails and has a trolley which moves transversely between the rails. A telescoping mast with a grapple at the bottom end is carried by the trolley so that fuel bundles may be accurately moved underwater to and from the reactor core.
The telescoping mast includes a plurality of nested tubes. An outer tube is fixed and the nested inner tubes extend downward from and retract into the outer tube. Each nested tube is smaller in diameter than the preceding tube. Because of the telescoping design, the smaller mast sections cannot begin to extend until the larger mast section above it reaches full extension.
Prior to use in the reactor, the mast and grapple are tested for operation in the fuel storage pool. The grapple jaws are tested using a dummy fuel bundle. The mast is slowly extended to the bottom of the fuel storage pool and checked for binding. However, due to the low depth of the fuel storage pool, the mast cannot reach full extension. In order to fully test the mast, some methods were tried, unsuccessfully, to hold the larger sections from extending to permit the smaller sections to extend. One method tried was to wedge the upper sections together to prevent extension. Another method tried was to tie the upper section to an object such as a handrail with a rope.
It is desirable to provide an apparatus that would permit the extension of the smaller sections of the mast in the fuel storage pool to fully test the mast before the refueling operation is started.
A retaining tool for a telescoping refueling arm in a nuclear reactor permits fully testing the mast before the refueling operation of the reactor is started. The refueling arm includes an outer tube assembly, a plurality of intermediate tube assemblies, and an inner tube assembly. Each of the outer tube assembly and the intermediate tube assemblies includes, at a bottom end, a flange and a plurality of roller housings spaced around the circumference of each flange. In an exemplary embodiment, the retaining tool includes a plurality of support members coupled to a plurality of plates. The retaining tool includes a first plate having a first and a second side, a second plate spaced apart from the first plate, and a third plate having a first and a second side The third plate is spaced apart from the second plate so that the second plate is located between the first and third plates. The second side of the first plate engages the roller housings of the mast outer tube assembly, and the first side of the third plate engages the roller housings of one of the intermediate tube assembly.
The above described retaining tool permits the extension of the smaller sections (the inner and one of the intermediate tube assemblies) of the mast in the fuel storage pool to fully test the mast before the refueling operation of the reactor is started.